had those faculae chiefly or entirely on the
left, 508 showed a nearly equal distribution, while 45 only had faculous
appendages mainly on the right side.[455] Now the rotation of the sun,
as we see it, is performed from left to right; so that the marked
tendency of the faculae was a lagging one. This was easily accounted for
by supposing the matter composing them to have been flung upwards from a
considerable depth, whence it would reach the surface with the lesser
_absolute_ velocity belonging to a smaller circle of revolution, and
would consequently fall behind the cavities or "spots" formed by its
abstraction. An attempt, it is true, made by M. Wilsing at Potsdam in
1888[456] to determine the solar rotation from photographs of faculae had
an outcome inconsistent with this view of their origin. They
unexpectedly gave a uniform period. No trace of the retardation poleward
from the equator, shown by the spots, could be detected in their
movements. But the experiment was obviously inconclusive;[457] and M.
Stratonoff's[458] repetition of it with ampler materials gave a full
assurance that faculae rotate like spots in periods lengthening as
latitude augments.

The ideas of M. Faye were, on two fundamental points, contradicated by
the Kew investigators. He held spots to be regions of _uprush_ and of
heightened temperature; they believed their obscurity to be due to a
_downrush_ of comparatively cool vapours. Now M. Chacornac, observing,
at Ville-Urbanne, March 6, 1865, saw floods of photospheric matter
visibly precipitating themselves into the abyss opened by a great spot,
and carrying with them small neighbouring maculae.[459] Similar instances
were repeatedly noted by Father Secchi, who considered the existence of
a kind of _suction_ in spots to be quite beyond question.[460] The
tendency in their vicinity, to put it otherwise, is _centripetal_, not
_centrifugal_; and this alone seems to negative the supposition of a
central uprush.

A fresh witness was by this time at hand. The application of the
spectroscope to the direct examination of the sun's surface dates from
March 4, 1866, when Sir Norman Lockyer (to give him his present title)
undertook an inquiry into the cause of the darkening in spots.[461] It
was made possible by the simple device of throwing upon the slit of the
spectroscope an _image_ of the sun, any part of which could be subjected
to special scrutiny, instead of, as had hitherto been done, admitting